I put a little time into the new maps, starting with Combat Training on each map and then playing Domination for a little while. Here we go:
Berlin Wall (played Domination & Combat Training): Will be a very cool objective map. The B-Dom flag is in the safe path going through No Man's Land. IMO, the team with better tactics (and a couple runners to get to B first) will do best at holding B flag. The safe passage is ripe for gas, stuns, and well timed nades.
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It is a pretty large map with a lot of enclosed areas and some elevated rooms/catwalks too. I fear on TDM and FFA there will be a lot of camping. There is some opportunity for sniping on this map, but not much.
I haven't tried Marathon/LW to get through No Man's Land. I played around in it just a bit in Combat Training and the sentry guns aren't surgical, you've got some leeway to avoid being killed for sure.
I would liken this map to Overgrown from MW1/MW2, though a bit smaller.
Stadium (played Domination & Combat Training): This map seems like it would be large, but is actually rather small. As 3arc said, this will be a good run & gun map. You'll either need to move fast and loud, or slow and quiet. There are some prime camping spots around the flags. Bombing game types will be really difficult on this map without a coordinated team to cover a bomb planter. It's fun, but not impressive.
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Kowloon (Played Combat Training only): This is going to be either really fun or really frustrating for people. There is a huge amount of elevation change and lots of small, winding routes through each level. The only long lines of sight are really from higher elevation to lower elevation. I think a good sniper with a silencer and motion sensor to watch his back has a good shot on this map.
There WILL be camping on this map in TDM. I have a feeling that explosives will play an even larger role in this map for Domination. CTF should be a lot of fun though, with the many different routes and elevation changes. Bombing game modes will be fun, but the team with the proper strategy will dominate. I'm thinking properly placed claymores and tactical insertion will make for a strong showing when planting & defending a bomb.
I tried the zip line once. Unless you have a teammate clear the landing zone with napalm/B52, you will probably die. A ghost might be able to slip down it and surprise the enemy team, if they're already distracted.
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Discovery (Played Combat Training only): I think this map is really cool. It is pretty spread out, with every major artery becoming a potential choke point if properly monitored. There are several small, medium, and large buildings for players to setup in. The paths and buildings also created some peripheral corners that could turn into a good spot for campers or sentry guns.
There is a central building that I expect will overlook the B flag, which should be very important to control in order to keep the B flag. I think this map will be KICK ASS in Ground War. With lots of players to control the various avenues connecting each side of the map, you could have a fun game of tug-of-war.
One of the spawn sides sits in front of a small building that a sniper could easily camp from. It has a pretty open view of the center of the map and the main building in the middle. It would be pretty easy for them to snipe from this room and have ample warning to defend themselves if someone approaches. Since this building is on the edge of the map, there's no back side to watch. I don't know if you would have visual of the B flag or a bomb site though.
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Map rotation: I played for ~45 minutes in Domination mode. Everyone voted random if an old map was up next in the rotation. We ended up getting new maps a little less than half the time I'd say; maybe 1/3 to be conservative? 3arc did say they increased the frequency at which you should get one of the new maps in the rotation.
Unfortunately the team I played against for most of the maps was pretty shitty. I'm interested to see how they go with some good players!